. Functional role, cellular source, and tissue distribution of rat elastase-2, an angiotensin II-forming enzyme. Am J Physiol Heart Circ Physiol 285: H775-H783, 2003. First published April 24, 2003 10.1152/ajpheart.00818. 2002We recently described a chymostatin-sensitive elastase-2 as the major angiotensin (ANG) II-forming enzyme in the perfusate of the rat mesenteric arterial bed (MAB) with the same cDNA sequence as rat pancreatic elastase-2. The role of this enzyme in generating ANG II was examined in the rat isolated and perfused MAB. The vasoconstrictor effect elicited by ANG I and the renin substrate tetradecapeptide was only partially inhibited by captopril but abolished by the combination of captopril and chymostatin or N-acetyl-AlaAla-Pro-Leu-chloromethylketone (Ac-AAPL-CK; inhibitor originally developed for human elastase-2). The effect induced by [Pro 11 ,D-Ala 12 ]-ANG I, an ANG I-converting enzyme (ACE)-resistant biologically inactive precursor of ANG II, was blocked by chymostatin or Ac-AAPL-CK. It was also demonstrated that cultured rat mesenteric endothelial cells synthesize elastase-2 and that mRNA for this enzyme can be detected in different rat tissues such as the pancreas, MAB, lung, heart, kidney, liver, and spleen. In conclusion, the demonstration of a functional alternative pathway to ACE for ANG II generation in the rat MAB and the fact that cultured MAB endothelial cells are capable of producing and secreting elastase-2 represent strong evidence of a physiological role for this enzyme in the rat vasculature. endothelium; chymostatin SEVERAL STUDIES HAVE POSTULATED the existence of alternative pathways to angiotensin (ANG)-converting enzyme (ACE) for ANG II generation in tissues of different species based on evidence derived from experiments carried out with a combination of protease inhibitors and ANG II receptor antagonists. In a pioneering study (9) in this area, it was demonstrated that the vasoconstrictor response induced by ANG I in blood vessels of the hamster cheek pouch was blocked only partially by ACE inhibitors but completely abolished by ANG II receptor antagonists, leading to the conclusion that this vascular bed converts significant amounts of ANG I to ANG II by a route that does not involve ACE. In other investigations, the partial or total blockade of ANG II formation by different combinations of ACE inhibitors with chymostatin or other protease inhibitors has provided clues as to the nature of the enzymes involved in ANG I conversion in a particular tissue or pharmacological preparation (23,45). Since the advent of [Pro 11 ,D-Ala 12 ]-ANG I, a biologically inactive precursor that selectively yields ANG II on incubation with chymases but not with ACE or carboxypeptidases (22), several reports (18,22,26,38,41,43,61,63) have described the relative contribution of chymases in ANG II formation in isolated preparations derived from various species.The vascular endothelium actively participates in the control of vascular tone through the synthesis and metabolism of seve...